Extracellular RNA (exRNA) from pathogens plays a key role as activator of innate immunity in mammals. However, the presence of host exRNA in serum and other body fluids challenges the current models of RNA based immune recognition. To understand its basis of specificity, it is important to catalog host exRNAs and their associated proteins in serum, investigate mechanisms leading to circulating ribonucleoprotein (RNP) homeostasis, and identify protein factors contributing to cellular RNA release. Genetic alterations in RNA targets or interacting proteins may contribute to imbalances in normal versus stress-triggered release of RNPs and push adaptive long-term pathogen-directed immunity towards autoimmunity. ExRNAs may also play a broader role in extracellular signaling similar to peptide hormones, which would also be captured by this experimental approach. This application brings together a team of multiple investigators with complementary expertise and history of close collaboration to build a solid foundation regarding identification, mechanism and function of extracellular RNAs and the proteins involved in their biogenesis, export, recognition, and turnover. The specific aims of the proposed project are: 1. Catalogue and quantify all classes of extracellular RNAs in human serum from normal subjects using various established and novel RNA seq approaches and examine normal variability of circulating RNA profiles within an individual, between individuals and the influence of gender, age, race, and disease. Establish a core facility for processing and archiving clinical materials (Williams, Putterman, Tuschi). 2. Determine exRNA composition in patients suffering from systemic lupus erythematosus (SLE), for whom antibodies against different classes of RBPs is a hallmark. Considering that these RBPs alter their subcellular localization upon stress and appear in stress granules with immature RNA and/or RNA targeted for turnover, we will evaluate in as much the composition of RNPs in stress granules harvested from immortalized B cells of normal and SLE subjects possesses immunostimulatory function and if these RNP granules are also released during stress (Tuschi, Putterman, Williams). 3. Develop a molecular and mechanistic understanding of stress granule formation and RNA/RNP mediated innate immune responses. Identify the RNA targets and RNP structures of autoantigens in tRNA stress responses, their turnover, and their immune receptors.